Pest Damage on Rose March 21 31 March 11 20 March 1 10 April 21 30 April 11 20 April 1 10 May 21 31 May 11 20 May 1 10 June 21 30 June 11 20 June 1 10 July 21 31 July 11 20 July 1 10 August 21 31 August 11 20 August 1 10 September 21 30 September 11 20 September 1 10 October 21 31 October 11 20 October 1 10 November 21 30 November 11 20 November 1 10 Green Fruitworm Botrytis Blight Cane Girdler Japanese Beetle Leafcutter Bees Leafhoppers Powdery Mildew Rose Chafer Rose Mosaic Virus Rose Rosette Roseslug, Bristly Roseslug Sawfly (Larva) Rust Spider Mite, Twospotted Aphids Black Spot KEY: fruit flower branches leaves trunk crown roots 125
Green Fruitworm Flower buds or developing fruit is completely devoured or partially damaged by chewing injury. Pale green worms with thin white lines and fine speckling on the skin may be present. There is only one generation per season with activity in May to early July. Worms may grow to a length of 1½ inches long. Locate and remove worms, or apply a microbial insecticide when worms are much smaller. Usually, green fruitworms are of little importance. Botrytis Blight Small flecks on petals; circular brown lesions on petals; petal tips or sides become brown and soft. Cankers develop on canes. Grayish-brown fungal growth (mycelium) on the plant. Prune out affected areas. Apply foliar fungicide when disease symptoms are present and repeat according to label instructions. Cane Girdler (Flatheaded Borer) Bronzy, one-quarter inch long adults emerge in May from D-shaped holes in old, swollen canes. New canes become swollen from larval girdling within and die back by late summer. Rugosa-type roses are susceptible to attack by beetles in May and June. Adult control is not feasible, as it usually coincides with blooming of flowers and pollinator activities. Prune swollen canes and destroy them during the dormant season, as they harbor borer larvae. Japanese Beetle Leaves are skeletonized, have ragged holes, or are completely eaten. Metallic green scarab beetles with coppery wings actively feed in clusters during the day. Pick off beetles in the early morning and drown in a bucket of soapy water. Spray foliage with neem oil as a deterrent. Capture beetles with a Japanese Beetle pheromone trap through the season. Spray beetles and foliage with an insecticide. Leafcutter Bees (Circular Holes) One-half inch circular holes are cut along leaf margins from May through August. Over time, nearly all foliage can be damaged in this way. Blackish leafcutter bees may be cutting the holes. Heavy damage may stress plants; cover them with fine mesh temporarily to discourage leafcutter bees. Apply neem oil only to the foliage in the late evening or early morning to repel bees, or temporarily treat foliage with an inert dust. 126
Leafhoppers Leaves develop pale flecks, which in time spread densely over leaf surfaces. Leaves may turn yellow. Wedge shaped adults, nymphs and fecal spots are present on leaf undersides. Nymphs cannot fly and are more easily controlled. A strong stream of slightly soapy water from a hose-end sprayer will dislodge and kill many. Other options include a horticultural spray oil, insecticidal soap, conventional insecticide, or systemic insecticide. Powdery Mildew Early symptoms are slightly raised red areas on upper leaf surface. White fungal growth (mycelium) appears as discrete patches on leaf surface. Young leaves may become twisted and distorted. Sanitation. Improve air circulation. Avoid planting in shady areas in the landscape. Apply foliar fungicides at disease onset. Rose Chafer These June beetles are tan, one-half inch long and slender, with long burntorange legs. They aggregate together to feed and mate. Leaves are skeletonized and flowers get ragged holes. Beetle activity is from late May to July. Insecticide applications may result in bee pollinators being killed. Rose chafer traps similar to Japanese beetle traps are available. Trap beetles in yellow or white buckets filled with soapy water. Cover prized plants with a mesh-cloth. Rose Mosaic Virus Chlorotic line patterns, ring lesions and mottling in leaves. Vein-banding may occur during prolonged periods of high temperatures. Infected plants tend to be less vigorous; more sensitive to winterkill. Remove infected plants. Use virus-indexed propagated plants. Rose Rosette Leaflet distortion and wrinkling. Bright red leaf pigmentation, witches broom. Phyllody. Canes are excessively thorny. Slow to mature. Remove infected plants. Use virus-indexed propagated plants. 127
Roseslug, Bristly (Sawfly Larva) Leaves are skeletonized in spring and summer, as there are two generations. Small, bristly, pale greenish caterpillars are usually present in May and July, and feed together. Inspect plants in early May and regularly until August. Examine leaves that are lower on the plant. In most cases, treatment is not needed, but where larvae are numerous and severe defoliation is expected, treat with an oil spray, insecticidal soap, or neem oil. Roseslug Sawfly (Larva) Leaves are skeletonized in late May through June. Slug-like, shiny, greenish, gregarious caterpillars are usually present on undersides of leaves. Inspect plants in early May. Be sure to examine leaves that are lower on the plant, and especially the undersides. In most cases, treatment is not needed, but where larvae are numerous and severe defoliation is expected, treat with an oil spray, insecticidal soap, or neem oil. Rust First appears on leaves as powdery masses of orange spores on lower leaves. Mature pustules appear as orange or brown lesions on upper leaves. Young stems and sepals may become distorted. Sanitation. Prune out affected areas. Apply foliar fungicide when symptoms are first observed and repeat according to label instructions. Spider Mite, Twospotted Leaves stippled or yellow with fine webbing on undersides of leaves. Tiny greenish mites moving beneath webbing. When foliage turns brown, mites may mass together at tips of stems. Populations explode during prolonged hot, dry weather. Monitor in late July, checking undersides of leaves. Keep host plants wellwatered. Dislodge colonies with a strong spray of water. Apply an insecticide/miticide if infestations become serious; repeat in 10 days. Aphids Leaves are yellow or become wilted; new growth is stunted. Abundant, sticky and glossy honeydew is secreted by aphids. Lady beetles and other natural enemies may be present. Treat if aphids are causing evident damage; otherwise, allow natural enemies to work. Dislodge early colonies with a strong spray of mild, soapy water. Control with a spray oil, insecticidal soap or insecticide. Apply a systemic insecticide early to realize benefit. 128
Black Spot Black lesions, circular or irregular in shape. Lesions have feathery margins; yellow halo surrounding the lesion. Premature defoliation. Sanitation. Prune out affected areas. Avoid overhead irrigation and excessive watering. Apply foliar fungicide once temperatures reach 72 F and repeat according to label instructions. 129